Uplink
A device wakes, sends a compact sensor message, and returns to sleep. This is the normal Sigfox direction.
Sigfox Uplink vs Downlink Asymmetry
Plan 140 uplinks, 4 downlinks, and device-initiated command windows
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An interactive Sigfox asymmetry workbench showing uplink quota, downlink request flow, payload limits, regional airtime caveats, and fit diagnosis for sensor-heavy IoT designs.
Sigfox is uplink-first, not a tiny always-on pipe
Build a one-day message plan and watch why sensor reports fit Sigfox better than command-heavy control. Downlinks are possible, but every one must be requested by a device uplink and only four sent downlinks fit the common daily contract.
140common device uplinks/day
4common sent downlinks/day
12 B / 8 Buplink max / downlink payload
24-Hour Uplink and Downlink Budget
A low-rate meter leaves most of the daily uplink budget unused and treats downlink as a rare configuration path.
5 / 140uplinks used
1 / 4downlinks sent
30.0 sRC airtime estimate
28:1uplink to downlink capacity
Report uplink
Request uplink
Sent downlink
Blocked or invalid
Downlink request
The network cannot simply push at any time. The device has to ask for an answer in an uplink.
Server answer
The Sigfox Cloud calls the customer server. A downlink is only sent if valid data is available.
Design fit
Good designs reserve downlinks for configuration, rare commands, or acknowledgments, not streaming control.
Pack uplink
Sensor data must fit the selected 0-12 byte uplink payload budget.
Transmit
The device spends uplink quota and radio airtime, then goes back toward sleep.
Ask for answer
A downlink opportunity exists only when an uplink carries a request flag.
Cloud callback
Sigfox Cloud asks the customer server whether an answer is ready.
Network emits
A valid answer consumes one of the four common daily downlinks.
Diagnose fit
Over-quota, invalid payload, or command-heavy traffic points to another link type.
Uplink Budget
Downlink Budget
Payload Fit
Formula Trace
Compact Quick Reference
| Question | Working rule | Design implication |
|---|---|---|
| How many uplinks? | 6 per hour, commonly 140 per device per day after protocol reserve. | Periodic sensor reports fit; chatty telemetry does not. |
| How many downlinks? | 4 sent downlinks per day in the common contract model. | Reserve them for configuration and rare acknowledgments. |
| Can cloud push anytime? | No. The device must first request a downlink in an uplink. | Commands wait for the next planned request window. |
| Payload sizes? | Uplink carries up to 12 bytes. Downlink payload is 8 bytes. | Pack binary fields and avoid text or bulky commands. |
The 140/day explanation is based on the RC1/ETSI teaching example: 1% of an hour is 36 seconds, six full messages per hour is 144 per day, and four are kept for protocol use. Regional radio configurations and contracts can differ.
Primary Source Anchors
- Sigfox Technical Quickstart - common uplink/downlink contractual limits.
- Sigfox Qualification - 140/day derivation, regional caveat, bandwidth and rate notes.
- Sigfox Payload - 12-byte uplink, fixed 8-byte downlink, padding and frame-time tiers.
- Sigfox Downlink Information - device-managed downlink request sequence.
- Sigfox Acknowledge Callback - quota, invalid payload, and request error codes.
Guided Practice
- Start from Water meter and note the spare uplink and downlink budget.
- Switch to Downlink overuse and watch the first four answers differ from blocked answers.
- Set Server response mode to No answer available. Requests still spend uplinks, but sent downlinks stay at zero.
- Raise sensor reports above 140/day. The fit diagnosis should reject the design even before downlink pressure matters.
Deeper Technical Notes
Why requests and sent downlinks are different
A device may request many downlink opportunities by setting the request flag in uplinks. If the server has no payload ready, the request does not become a sent downlink, but the request uplink still counts against the uplink budget.
Why payload bytes change airtime
Sigfox uplink transmissions use predefined payload length tiers. A 9-byte useful payload occupies the 12-byte tier, so it takes the same frame time as a full 12-byte payload in the teaching model.
What the animation simplifies
The timeline is a planning model. Real deployments also depend on local radio configuration, coverage, contract terms, backend callback behavior, and operator policy. Use the source links and local operator guidance before committing a product design.